A drop-bottom hopper car is mainly used fir carrying bulk cargo on a railway line and is designed to unload the bulk cargo either onto a conveying belt or into a pit between rails in a bottom dump manner after the car arrives at a destination. A discharge door (called as “bottom door”) at the bottom of the existing drop-bottom hopper car is generally opened and closed by a five-rod-linkage eccentric self-locking mechanism (i.e. a bottom door opening-closing mechanism).
Since the unloading door of the drop-bottom hopper car is located at the bottom of the car body, the existing drop-bottom hopper car is provided with a secondary locking mechanism in order to prevent the bottom door from being accidentally opened during the transportation to unload the cargo onto the tracks and thus to cause danger to the traffic safety As shown in FIG. 1, the existing secondary locking mechanism includes two locking arms 3 and one secondary locking cylinder 5, wherein the two locking arms 3 are hinged onto a car body 1, and the secondary locking cylinder 5 is hinged between the two locking arms 3. After the two bottom doors 2 are closed, the secondary locking cylinder 5 retracts and brings the two locking arms 3 into rotation to shut till the locking arms 3 hook onto the respective transmission shafts 4 arranged on the bottom doors 2. When the car moves, the locking arms 3 are always kept in position, i.e. the secondary locking mechanism is ensured to be kept in a locking position. Thus, even when the bottom door opening-closing mechanism fails and the sealing function is lost, since the secondary locking mechanism is provided and kept in a locking position, the bottom doors 2 are prevented from being opened, so as to avoid the discharge of the cargo and to ensure the traffic safety.
Though the above-mentioned secondary locking mechanism can prevent the bottom doors from being opened accidentally, there is a need to mount the locking arms 3 and the secondary locking cylinder 5. Thus, both the manufacture cost and the maintenance cost are increased. Additionally, when the bottom doors are desired to be opened, the secondary locking mechanism is firstly actuated to unlock the bottom doors, and the bottom door opening-closing mechanism then follows to open the bottom doors. When the bottom doors are desired to be closed, the bottom door opening-closing mechanism is firstly actuated to close the bottom doors, and the secondary locking mechanism then follows to lock the bottom doors. As can be seen from the above, there is a logic order in the processes of the opening/closing of the bottom doors and the unlocking/locking of the secondary locking mechanism, so that a control system for controlling the opening/closing of the bottom doors 2 becomes relatively complicated.